Explosive



Patented Nov. 6, i934 UNITED STA Tss EXPLOSIVE Albert Stanley Fox, New Castle, and Floyd Rape, i

Edenburg, Pa., assignors to Burton Explosives, Inc., Cleveland, Ohio, a corporation No Drawing.

Serial No. 582,874

14 Claims.

1 This invention relates to explosives and more particularly to an improvement in explosives which may advantageously be used and illustrated in those of the permissible type as-em- 5 ployed in. coal mining. For the purpose of describing our invention or discovery the following specification will deal largely with low density explosives of the permissible type which may be regarded as the preferred environment and embodiment of our invention.

In the mining of coal, successful operation depends very largely on the production of a maximum proportion of lump coal to fines. For obtaining these results the explosive should combine strength, low rate of detonation, low density,

ample sensitivity and safety. Such an explosivev must also be safe, that is it should be difiicult to V ignite by flame or spark, and on explosion the gases produced must be sufficiently free from poisonous gas as not to endanger the health 01' lives of those working in the mine, and the flame of explosion must be of sufiicient short duration and of such low temperature as not to cause ignition or explosion of the gaseous and dusty atmosphere in the mine.

Explosives of this type to which our invention is particularly applicable consist of a sensitizer such as nitroglycerin or other liquid explosives, or a mixture of them, with or without nitrohydrocarbons or nitrated carbohydrates, an oxidizing agent or agents such' as nitrates, perchlo: rates, chlorates and the like, a carbonaceous combustible absorbent, or a combination of such absorbents, a cooling agent if required, or a com- 40 bination of cooling agents, such as chlorates or oxalates, and a small portion of an antacid material which is generally chalk.

It is commonpractice to regulate in part the rate of detonation of such explosivesby varying the fineness of the ammonium nitrate used, relatively fine grains! giving a fast rate, whilst relatively coarse grains give a slow rate. By "relatively fine grains is meant ammonium nitrate of such fineness that at least approximately 40 per cent will pass a 100 mesh sieve, and not more than 5 percent will be retained on a 40-mesh sieve; by relatively coarse grains is meant ammonium nitrate of such fineness that less'than approximately 5 per cent passes through a 60- mesh sieve. By fast rate is meant approxi-.

mately 2500 meters per second or over, and slow rate has heretofore meant below 2500 and as 10 as about 1900 meters per second.

It has however not been possible with the carbonaceous combustible absorbents hitherto in use, to produce a low density explosive, that is an explosive having a high cartridge count, which has a rate of detonation lower than about 1900 meters per second, while retaining a safe and workable degree of sensitivity.

Furthermore, all heretofore known absorbents for nitroglycerin or the like have had distinct limitations which we by our invention or discovery have been able to overcome to a surprising degree and with most beneficial and useful results. Powders employing wood pulp have too great density and thus too low cartridge count. Powders in which bagasse or the like have been substitutes for wood pulp, while having lower density, have by reason of the high absorption value of the low density absorbent, been relatively insensitive particularly where it has been desired to obtain a low rate of detonation.

It is therefore among the, objects of our invention to provide an absorbent for the liquid explosive ingredient of an explosive composition which has a low density so that high cartridge count can be maintained which at the same time has a relatively low absorption value so that satisfactory sensitivity can be maintained particularly in the ranges of very low rates of detonation.

Another object of our invention is to provide a carbonaceous absorbent material which in relatively finely divided form, where for example substantially all of the particles will pass through a twenty mesh sieve and be retained on a forty mesh sieve, is non-friable so that the size, shape and physical structure of the particles is not materially altered during the process of manufacture of the explosive. This, of course, insures a uniformity of product both with respect to the characteristics of separate cartridges of the same batch and with respect to various parts of the same cartridge.

Another object of our invention is to provide an explosive powder which can be readily packed or tamped into cartridges but which as far as the absorbent material is concerned will not produce hard cartridges or cartridges with hard portions.

One of the more general objects of our invention is to produce an explosive or dynamite of the permissible type which for a given strength and sensitivity has a low rate of detonation and a high cartridge count.

Another object of our invention is to provid a powder of the permissible type having a very low rate of detonation and. relatively low density.

while maintaining a good sensitivity. L

Other objects include the provision of an absorbent for the liquid explosive ingredient in an explosive composition which can be depended upon to be consistent in its characteristics of structure and performance over a relatively long period of time.

Other'objects will appear from the following description of a preferred embodiment of our invention which we illustrate herein particularly in the environment of dynamite or explosive of the permissible type. The essential characteristics are summarized in the claims.

In carrying out the objects of our invention, we have found that hemp hurds particularly those treated as we will presently describe, have the property or combination of properties not possessed by other heretofore known absorbents for the liquid explosive ingredients and particularly those qualities or properties not heretofore'found in the various low density absorbents such as bagasse, balsa wood and the like, which property or combination of properties, it is our invention or discovery, make hemp hurds the material particularly suitable for use as the absorbent in explosive compositions having a liqui explosive ingredient.

Hemp hurds are obtained in the production of hemp by crushing the dry stalks of the hemp plant (Cannabis sativa L) from which hemp fibre is separated by scutching. The hemp stalkis hollow with a cylindrical woody shell of hard thick walled cells, and the hurds are found, after the crushing process, in lengths varying from approximately one-half 'to three inches, andwhich in crushing are mostly split into numerous segments. a

The hemp hurds as obtained after the hemp has been removed are, in carrying out the objects of our invention, reduced to small fragmentary particles by grinding or chopping. Preferably these particles are of such size that substantially all of them areretained on a forty mesh sieve. In the preferred embodiment of our invention, to wit, in the production of low density explosive of the permissible type, we then treat the finely divided hemp hurds preferably by soaking them in water for a few hours and then boiling them at atmospheric pressure for about an hour and a half, albeit we contemplate that this treatment may be donebefore the grinding or chopping operation. The soaking as such has not been found to be essential albeit we find it a preferable step in treating the durds. After boiling, the hurds are then dried and of the dried hurds, in the preferred form at our invention, to wit, making low density ex- Jlosives, we prefer to use those particles sub- ;tantially all of which pass through a twenty- ?nesh sieve and substantially all of which are retaned on a forty mesh sieve.

We have found the thus finely divided hemp lllIdS before treatment, to have a density of about 0.2, measured in the same manner in which ve find for example, the density of that grade of vood pulp which has the lowest absorbency, to e 0.25 to 0.29, of balsa wood flour about 0.13, f that grade of bagasse which has the lowest .bsorbency about 0.15 to 0.16, and of sphagnum moss about 0.1. After treatment we find by the same method of measuring, that hemp hurds have a density of about 0.14 which for all practical purposes it is seen is about the same density treated above have the capacity for absorption of nitroglycerin such that a unit of mass of hemp hurds absorbs about 2.6 times its weight of nitroglycerin. By the same manner of measuring absorption of nitroglycerin, We have found that wood pulp absorbs about 2.3 to 3.3 times its weight of nitroglycerin, whereas the other low density absorbents, noted above, such as balsa wood, bagasse and the like, absorb about 5.6 times their weight of nitroglycerin.

It will thus be seen that the hemp hurds have as regards absorption of nitroglycerin and density, the novel properties or combination of properties of having relatively low density and at the same time having relatively low ability to absorb nitroglycerin. The treated hurds have about the samedensity as the heretofore known light absorbents, but have a much lower absorption for nitroglycerin than do those absorbents. It will be noted that the absorption capacity of treated hemp hurds for nitroglycerin is less than one half of that existing in the heretofore known light absorbents, and is more accurately about m of that of those absorbents.

-The untreated hemp hurds, that is the hurds which have not been reduced in density have a density of about 0.2 and thus stand about midway between wood pulp and the other well known light absorbents in density and differ from those absorbents particularly in having an absorption capacity for nitroglycerin as little as that of the least absorbent wood pulp, i. e. about 41% of that of those light absorbents.

While we prefer to use the treated hemp hurds, particularly in the manufacture of lowdensity explosives, it will be appreciated thatthe untreated hurds have much the same beneficial properties as the treated hurds, differing from the treated hurds principally in density. We contemplate that theuntreated hurds may and in many instances should-be used in preference to the treated hurds, all within the major precepts of our invention or discovery, particularlyin the production of powders where the maximum low density is not sought.

It is our invention or discovery that where the whole or part of the heretofore known carbonaceous combustible absorbent material is replaced by finely divided hemp hurds, the resulting explosive composition has vastly improved and very valuable properties which make possibe the carrying out of theobjects of our invention. I

As noted above, the ground or fragmentary particles of hemp hurds have relatively low density which is essential for the production of low density or high count explosives. 0n the other hand, the hemp hurds differ from all heretofore known low density absorbents in that theirapacity to absorb nitroglycerin or other liquid explosive ingredient is relatively low, the hemp hurds absorbing only approximately one-half the weight of 'nitroglycerin that such well known low density absorbents as bagasse, corn stalks, sphagnum moss and balsa wood meal do. The

absorption valueof hemp hurds, with regard to I nitroglycerin, is roughly about the same as that 'of the least absorbent common wood pulp, but

the density of hemp hurds, particularly those treated as described above, isvery much less than the density of wood pulp. The combination of these two properties viz. relatively low density and low absorption, which combination is not possessed by the other known absorbents, makes hemp hurds particularly useful and advantageous in the manufacture of explosives. E

An absorbent of relatively low density is necessary in the production of low density-explosives, that is of explosives having a relatively high'cart'ridge count, usually expressed as the number of 1%" x 8" cartridges per 100 pounds; Relatively low absorption, which is an outstanding property of hemp hurds, is of great advantage in preserving sensitiveness to propagation of explosives, because, as we believe, the unabsorbed nitroglycerin spreads itself in a thin film over the other constituents of the explosive and helps to propagate the explosive wave throughout the whole mass. It also permits when required, the use of higher proportions of the absorbent, and lower proportions of nitroglycerin, thereby decreasing the density of the explosive or increasing the cartridge count, and decreasing its rate of. detonation, while at the same time maintaining high 'sensitiveness to propagation.

The hard cellular structure of hemp hurds makes the ground or chopped granular material relatively non-friable, whether treated as above described or not, reduces the tendency of this e. g. bagasse, sphagnum moss, corn stalks, etc.,'

is to break down into smaller particles in relatively hardmasses during the above mentioned manufacturing operations, thereby increasing both the density and the rate of detonation of the explosive, and also causing'the production of relatively hard cartridges in the operation of cartridge packing.

An outstanding property of low density explosivessuch as permissible dynamites containing hemp hurds, is their low rate of detonation.

" We have obtained /by using treated hemp hurds cartridges, unconfined.

Though our invention is applicable to the manufacture of explosives other than thoseof the low density permissible type, we give hereunder forthe purpose of illustration, examples of several low density explosives of the permissible type embodying the precepts of our invention in its preferred form using treated hemp hurd particles.

7 M In the following table several formula of low A B G D E Percent Percent Percent Percent Percent Nitroglycerin 0 8.5 8. 5 l2. 0 12. 0 Relatively coarse am- -momum nitrate 76. 0 75.0 73.0 66. 5 65. 5 Sodium nitrate 4. 0 4. 0 4. 0 5. 0 5. 0 Treated hemp hurds 10. 5 l2. 0 14.0 16. 0 l7. 0 Chalk 0. 5 0. 5 0. 5 0. 5 0. 5

Weight of 1% x 8" cartridges in grams. 122 113. 4 110. 5 103 90 1%" x 8 cartridges per 100 lbs 372 400 410 440 504 Rate of detonation in a meters per second 1470 1290 122i 1460 1290 Thus far our tests and observation of powders made according to these formulae indicate that powders A, B, and D are highly sensitive; powder E somewhat less sensitive although safely high, and powder C high enough for good propaga: tion but lowerthan the others and indicating ,to us that we were. approaching in powder C a lower limit of sensitivity where the nitroglycerin content should preferably be increased if the density of the dynamite of this type were to be further reduced by increasing the hemp hurd content.

Examination of the foregoing table shows the novel and advantageous resultsthat can be obtained in thepractice of our invention. For example, those skilled in the art. will appreciate that very minor changes in the formulae above will give a series of low density permissible dynamites of substantially the same strength in which the cartridge count can be varied from about 350 to over 500, 1%" x 8" cartridges per .100 pounds, all having a .rate of detonation between about 1500 and 1200 meters per second, and all being far more sensitive particularly in these i unique ranges of combined high count and low rate than have ever before been attained.

It will be understood that the compositions stated above are given only'as examples, and that we may vary proportions considerably and introduce other materials without departing from the spirit of our invention. By nitroglycerin we mean to include the use of other liquid explosives used usually with the object of producing low freezing explosives, and for the same reason we'include the use of: nitrohydrocarbons or nitrated carbohydrates, or both, dissolved in the nitroglycerin or other liquid explosive. We may also use a relatively small: proportion of nitrocotton, which is commonly used when a plastic or semi-plastic explosive is required, and which will be more water resistant. We-may replace the whole or part of the sodium nitrate by other suitable oxygen carrier, or by a cooling agent, such as sodium chloride, ammonium chloride'or ammonium oxalate. We may also replace part. of the hemp hurds by other suitable carbonaceous combustible absorbents.

For permissibleexplosives the most. important ranges in compositions are as stated. hereunder:

, I v Percent Nitroglycerin s 6 to 16 Nitrocotton 0 to 1 Ammonium nitrate 50 to 85- Sodium nitrate 0 to 20 Sodium'chloride l 0 to 20 Ammonium chloride--. 0 to 20 Hemp hurds.. i 3 to 20 Chalk 0 to 0.5

' As already stated, our invention is particularly useful and advantageous in the manufacture of low density explosives of the permissible type, but it may be applied and used in the manufacture of other dynamites and high explosives by applying the major precepts of our invention to other well known kinds and classes of dyliamites and explosives.

While the foregoing illustrates and describes essentially a preferred form of our invention, modifications and improvements will occur to those skilled in the art without departing from the spirit thereof and we do not wish to be so limited in this or in any manner other than by the claims appended hereto.

We claini:

1. An' explosive having a liquid explosive ingredient and having as an absorbent thereforhemp hurds treated to reduce the density thereof.

2. An explosive having a liquid explosive ingredient and-having as an absorbent therefor hemp hurd particles treated to have a density less than 6.15 and a capacity for absorption of no more than about.2.6 times its weight of nitroglycerin.

3. An explosive having a liquidexplosive ingredient, ammonium nitrate and hemp hurds treated ,to reduce the density thereof as an ab-,

sorbent for said liquid ingredient.

4. An explosive having a liquid explosive ingredient, ammonium nitrate and finely divided hemp hurds treated to reduce the density thereof as an absorbent for said liquid ingredient.

5. An explosive having a liquid explosive ingredient and an absorbent comprising flnely divided hemp hurds treated to reduce the density thereof in particles substantially all of which pass through a twenty mesh screen and substantially all of which are retained on a forty mesh screen. 1 p

6. An explosivehaving a liquid explosive ingredient, an absorbent comprising finely divided hemp hurds treated to reduce the density thereof in particles substantially all of which pass through a twenty mesh screen and substantially all of which are retained on a forty mesh screen, and ammonium nitrate crystals.

7. An explosive having a liquid explosive ingredient, relatively coarse ammoniumv nitrate crystals and an absorbent comprising hemp hurds having a density of about 0.14 and divided into particles which pass a twenty mesh screen and i of which about 90% are retained on a forty meshscreen.

8. An explosive having a liquid explosive ingredient, relatively coarse ammonium nitrate crystals and an absorbent comprising hemp hurds divided into fragmentary particles and having a density of about 0.14. p 9. An explosive having a liquid explosive ingredient and an absorbent therefor comprising hemp hurds having a density substantially as low as bagasse or balsa wood meal and having an absorption value for nitroglycerin substantially as low as that of the least absorbent wood pulp.

10. An explosive having a liquid explosive ingredient and an absorbent therefor comprisinghemp hurds having a density substantially as low as bagasse or balsa wood meal and having an absorption value for nitroglycerin about half that of bagasse or balsa wood meal.

11. An explosive composition having a liquid explosive ingredient, relatively coarse ammonium nitrate crystals and fragmentary particles of hemp hurds treated to reduce the density thereof as an, absorbent for the liquid ingredient, saidcomposition being of density such that morethan four hundred 1% x 8" cartridges weigh less than one hundred pounds.

12. An explosive composition having a liquid explosive ingredient, relatively coarse ammonium nitrate crystals andfragmentary particles of hemp hurds treated to reduce the density thereof as an absorbent for the liquid ingredient, said composition having a density such thatmore than four hundred 1%" x 8' cartridges weigh less thanone hundred pounds, having a relatively high sensitivity and a rate of detonation less than 1500 meters per second.

13. A low density dynamite of the permissible type, having a liquid explosive ingredient, and an absorbent therefor comprising hemp hurds treated to reduce the density thereof, said dynamite being fully'sensitive to propagation and having a rate of detonationdepending on the rel- .ative proportion of said ingredients as low as second.

- ALBERT STANLEY FOX. 

